The official gazette of Japanese Patent Laid-open Publication No. 1-117876/1989 discloses the process schematically illustrated below for the production of a tetrazole intermediate for antihypertensive compounds. ##STR1## This process comprises reacting the nitrile compound with an excess of trimethyltin azide, separating the crystalline trimethyltin tetrazole derivative from the residual trimethyltin azide by filtration and removing the trimethyltin group with hydrogen chloride to provide the desired tetrazole compound.
Japanese Patent Laid-open Publication No. 63-23868/1988 discloses the following process. ##STR2##
However, Process A described above is disadvantageous, as a commercial production process, in that the overall yield is only 78% and the process involves two reaction steps. Moreover, it is likely that some of the excess trimethyltin azide contaminates the trimethyltin tetrazole derivative produced. It is also likely that when the trimethyltin tetrazole derivative is hydrolyzed with hydrogen chloride, the contaminant trimethyltin azide is decomposed to give rise to the toxic and highly explosive hydrogen azide. Therefore, this process as a commercial process presents a serious safety problem.
On the other hand, in Process B, the range of compatible compounds is limited as compared with the organotin azide process. For example, in the case of a compound in which the substituent in the 2-position of the imidazole ring is a lower alkoxy group, there occurs a decomposition reaction to detract from the product yield. Moreover, since a sublimation of the explosive ammonium azide [N. Irving Sax, Richard J. Lewis, Sr., Dangerous Properties of Industrial Materials, Van Nostrand Reinhold (1989)] occurs during the reaction to cause deposition of the sublimed azide on the condenser or reactor ceiling, the process is less suitable for commercial exploitation from safety points of view.
In either process, it is common practice to use the azide compound in excess for improved yield and reduced reaction time but when the reaction mixture is acidified, the toxic and highly explosive hydrogen azide is released from the unreacted azide compound present in the reaction system.
Since this hydrogen azide is a volatile liquid (boiling point: 37.degree. C.), it is obvious that the worker handling it is exposed to a constant risk. It is reported that hydrogen azide administered in a dose of 0.05 to 0.1 mg/kg induces prostration in man. Moreover, while hydrogen azide as such is a highly explosive substance, it is known that the presence of this substance even in solution at a concentration over 17% is a dangerous cause of explosion, suggesting that an organic composition or system containing this substance at a substantial level is also a major source of hazard. It is also known that hydrogen azide forms explosive salts with heavy metals.
Particularly when an organotin azide such as a trialkyltin azide or triphenyltin azide is employed, the step of hydrolyzing the trialkyltin or triphenyltin tetrazole derivative with an inorganic acid to provide the tetrazole derivative requires a provision for stripping off the hydrogen azide originating from the excess organotin azide from the reaction system and trapping it with an alkaline solution, but since the procedure involved is complicated and very dangerous, the method cannot be utilized commercially.
Also, WO92/02508 discloses the following process. ##STR3## This process comprises reacting the nitrile compound with tributyltin azide and removing the tributyltin group without isolation of the tributyltin tetrazole derivative by addition of aqueous mineral acid to the reaction mixture.
However, tributyltin azide is high in vapor pressure (b.p. 118.degree.-120.degree. C./0.18 mmHg) and has a powerful odor. This odor is an extraordinarily peculiar one, which is readily absorbed by other materials, for example, clothes of workers, reaction vessels or drying machines, and, which, once absorbed, is hard to remove. Besides, tributyltin azide causes, once touching on the skin directly, flush area on the skin, giving rise to rash symptoms such as itching or blisters.
Further, it is known that lower alkyl tin compounds are generally highly toxic [N. Irving Sax, Dengerous Properties of Industrial Materials (1989)]. While tributyltin azide is usually synthesized from tributyltin chloride and sodium azide, the starting tributyltin chloride has also a powerful odor and causes rashes, and its toxicity is so strong as to produce an LD.sub.50 129 mg/kg (rats, p.o. Albright and Wilson Ltd., Technical Service Note, "Tributyltin Chloride--Safety and Environmental Protection," March, 1977). Further, tributyltin chloride is absorbed also from the skin.
The workers using tributyltin azide are exposed to a constant risk of hazard such as its peculiar odor absorbed into their clothes, troublesome processes of washing the machines and tools, appearance of rash, odor of the starting material, toxicity and danger of its absorbance from the skin. Therefore, it is difficult to use tributyltin azide on an industrial scale, from the viewpoint that the safety of the workers is not ensured.